1. Field of the Invention
The invention relates generally to systems and methods for powder coating, and more specifically to a symmetrical multi-port powder injection ring.
2. Discussion of Background Information
A variety of thermal spray coatings are commonly used to protect various types of components. Coatings may provide various benefits such as, for example: resisting wear, inhibiting corrosion, controlling clearances, salvaging worn components, resisting high temperatures, enhancing electrical properties, etc. These benefits can differ based on the coating material type and how those materials are applied. One group of thermal spray coatings to which the subject matter of the present invention pertains in particular are those applied via the plasma spray process. This process has been used to apply many different types of coatings in numerous industries.
The plasma gun is commonly used as a process tool in the spray coatings industry due to the wide range of parameters that are achievable with this basic tool. The plasma thermal spray process basically involves spraying molten or heat softened material onto a substrate to form a coating. Feedstock material, typically in powder form, is injected into a high temperature plasma flame, also known as a plasma plume, where it is rapidly heated and accelerated, and subsequently impinged on a substrate that is intended to be coated.
In conventional plasma guns, the plasma plume is created using an arc internal to the gun and guided through an internal channel to an outlet nozzle. Powder for forming a coating onto a substrate is injected into the plasma plume by at least one powder injector. The powder injector may be located internally, e.g., prior to the outlet of the nozzle, or externally, e.g., downstream of the nozzle exit.
In conventional thermal spray devices, a known source of inefficiency is the fact that a large amount of the kinetic and thermal energy produced by the plasma gun is not transferred to the injected powder. Attempts at consuming this energy by simply increasing the amount of powder injected, for example by increasing the powder feed rate at each powder port and/or by increasing the number of injectors have resulted in a reduction of quality of the coating, as well as powder buildup on the face of the gun nozzle and the powder injectors. Similarly, attempts at solving the injection problem by using internal injection have resulted in powder buildup internal to the gun bore or inside the powder injectors.
As such, powder buildup on surfaces of the plasma gun is a problem with both internal and external powder injectors. Powder that is built up on hardware surfaces, e.g., surfaces of the powder injectors, surfaces of the plasma gun, etc., causes inefficiency by requiring that the plasma gun be shut down more often for cleaning. Additionally, powder buildup is indicative of an overall process inefficiency, since powder that is deposited on the plasma gun and other hardware is powder that does not get deposited as coating on the target substrate.
Accordingly, there exists a need in the art to overcome the above-noted deficiencies.